1. Field of the Invention
The present invention relates to an image forming apparatus such as a laser printer or an electronic copying machine having a recycling mechanism for returning a toner recovered by a cleaning unit to a developing unit.
2. Description of the Related Art
A laser printer having a recycling mechanism for returning a toner recovered by a cleaning unit to a developing unit has been conventionally developed. In a laser printer of this type, however, since an amount of a toner to be released is temporarily increased by a vibration produced when a cover of a main body is opened/closed to replace a photosensitive body or a fixing unit, a toner concentration in a developing unit becomes nonuniform. Therefore, if the laser printer performs an image forming operation in this state, a defective image is undesirably formed.
For this reason, in an image forming apparatus having such a recycling mechanism, when a cover is opened/closed, a toner is forcedly circulated to uniformize variations in toner concentration. However, this method of uniformizing a toner concentration by forcedly circulating a toner requires a long time period before the toner concentration is restored to a reference value.